
package com.timber.util;


import javax.swing.SwingUtilities;


/**
 * This is the 3rd version of SwingWorker (also known as
 * SwingWorker 3), an abstract class that you subclass to
 * perform GUI-related work in a dedicated thread.  For
 * instructions on using this class, see:
 *
 * http://java.sun.com/docs/books/tutorial/uiswing/misc/threads.html
 *
 * Note that the API changed slightly in the 3rd version:
 * You must now invoke start() on the SwingWorker after
 * creating it.
 */
public abstract class SwingWorker
{
  private Object value;  // see getValue(), setValue()
  private Thread thread;

  /**
   * Class to maintain reference to current worker thread
   * under separate synchronization control.
   */
  private static class ThreadVar
  {
    private Thread thread;

    ThreadVar( Thread t )
    {
      thread = t;
    }

    synchronized Thread get()
    {
      return thread;
    }

    synchronized void clear()
    {
      thread = null;
    }
  }

  private ThreadVar threadVar;

  /**
   * Get the value produced by the worker thread, or null if it
   * hasn't been constructed yet.
   */
  protected synchronized Object getValue()
  {
    return value;
  }

  /**
   * Set the value produced by worker thread
   */
  private synchronized void setValue( Object x )
  {
    value = x;
  }

  /**
   * Compute the value to be returned by the <code>get</code> method.
   */
  public abstract Object construct();

  /**
   * Called on the event dispatching thread (not on the worker thread)
   * after the <code>construct</code> method has returned.
   */
  public void finished()
  {
  }

  /**
   * A new method that interrupts the worker thread.  Call this method
   * to force the worker to stop what it's doing.
   */
  public void interrupt()
  {
    Thread t = threadVar.get();
    if( t != null )
    {
      t.interrupt();
    }
    threadVar.clear();
  }

  /**
   * Return the value created by the <code>construct</code> method.
   * Returns null if either the constructing thread or the current
   * thread was interrupted before a value was produced.
   *
   * @return the value created by the <code>construct</code> method
   */
  public Object get()
  {
    while( true )
    {
      Thread t = threadVar.get();
      if( t == null )
      {
	return getValue();
      }
      try
      {
	t.join();
      }
      catch( InterruptedException e )
      {
	Thread.currentThread().interrupt(); // propagate
	return null;
      }
    }
  }


  /**
   * Start a thread that will call the <code>construct</code> method
   * and then exit.
   */
  public SwingWorker()
  {
    final Runnable doFinished = new Runnable()
      {
	public void run()
	{
	  finished();
	}
      };

    Runnable doConstruct = new Runnable()
      {
	public void run()
	{
	  try
	  {
	    setValue( construct() );
	  }
	  finally
	  {
	    threadVar.clear();
	  }

	  SwingUtilities.invokeLater( doFinished );
	}
      };

    Thread t = new Thread( doConstruct );
    threadVar = new ThreadVar( t );
  }

  /**
   * Start the worker thread.
   */
  public void start()
  {
    Thread t = threadVar.get();
    if( t != null )
    {
      t.start();
    }
  }
}
